I have used both..K systems about 7 years ago and Grippamax recently. So my experience with both is this.
K systems, tank and frame. Came across as a nice guy and is quite a bit cheaper. The frame was made my him with the bed type angle iron they use and painted, it did start to show signs of surface rust after a while also tank was standard wydale one.
Had an issue regarding that there was no lid for the tank and was promised it would get sent to me straight away but after a number of phone calls (was hard to get hold of him) i never received it. Also looking at where things were bolted down, frame was only bolted in 3 places 1 on each corner and the plates used underneath were just scrap pieces of metal (just cut from something and not painted for rust protection) although thick they were narrow and on 1 of the fixings you could see where the plate had twisted a bit and bent the floor slightly underneath.
Overall although cheap, my experience was you get what you pay for, i actually took it out after about a year after i got a second hand pure freedom frame and got them to fit it (far more solid and stainless steel frame).
Last year had a Grippamax tank and frame fitted although more expensive the quality is second to none as is there customer service. Tank is properly baffled and cant be compared to a wydale tank absolutely no rocking from the water when tank is half full, the frame to fix it down is solid and with the cabinet to hide all the pumps etc makes things neat and tidy. You can also bolt battery boxes to the side of the tank as the tank has a number of fixing points on it.
Just before Christmas i had the hot water system added when i got it back i did have a few issues with it, but an engineer came to my home address straight after Christmas and sorted it all out.
Its all down to what your preference is, cheap and cheerful then K systems would probably do, you want something crash tested neat and tidy and about as safe as it can possibly be with great costumer service then Grippamax, although i was also happy with the pure freedom installation just a shame they still use the wydale tanks.
The benefit of Aquafactors is you can have it made to your size and specification although i dont know what the fitting of them is like.
Personally i would say grippamax although probably the most expensive they are very well made and thought out and it can always be moved to another van in the future so no reason it cant last for many years.